Electrical contact brush for high altitude use



United States Patent 2,989,490 ELECTRICAL CONTACT BRUSH FOR HIGH ALTITUDE USE Dimiter Ramadanolf, Berea, Ohio, assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Feb. 19, 1 958, Ser. No. 716,009 13 Claims. (Cl. 252-503) This invention relates to brushes for the supply of electric current, and more particularly concerns long wearing commutator brushes which are suitable for use at conditions encountered at both sea level and at high altitudes.

For sea level and high altitude applications, metal graphite brushes, such as high altitude copper-graphite brushes, have several desirable properties. At a given current density and rubbing speed, the copper-graphite brushes generally operate with a lower contact voltage drop and a lower temperature at a given load than do high altitude electrographitic brushes. The brush stock has low electrical resistivity, which is helpful in cutting down power losses. But copper-graphite brushes also have some disadvantages. They operate with higher coeilicients of friction than electrographitic brushes, and are sensitive to commutator or ring eccentricity. Sometimes the combination of these two factors may intensify sparking, and even cause, under some conditions, the release of small streamers at the trailing edges which may lead to undesirable ring wear. Consequently, the conventional copper-graphite brushes are usually limited in their application.

It is, therefore, an important object of the present invention to provide an improved metal graphite brush composition which is not subject to this difliculty, either under atmospheric or high altitude operation.

Another object of the present invention is to provide an improved metal graphite brush suitable for use at varying altitudes, which will deposit a boundary lubricating film upon the commutator surface at both high and low altitudes, and which will not unduly wear the commutator during the life of the brush.

The conventional metal graphite brush containing approximately 25% to 75% copper, to 60% graphite, a small amount of binder material and 5% to 25% of a compound selected from the group consisting of barium fluoride, strontium carbonate and calcium carbonate has some unusually good properties as a high altitude brush, for example, a brush of the above noted type having a composition of about 75 percent copper, 15 percent graphite and 10 percent barium fluoride has an electrical resistivity of 0.000008 ohm per cubic inch. Its contact voltage drop of 035 volt with a current density of 180 amperes per square inch at an altitude of 40,000 feet above sea level is one of the lowest on record. Such a brush grade has proven to commutate very well, and due to its barium fluoride content, has resisted dusting ataltitudes up to 70,000 feet. A weakness possessed by this copper graphite brush which is representative of the behavior of brushes falling within the above composition range is its short life under some conditions. It has an average brush life of only 825 hours per inch at sea level, and 425 hours per inch under simulated altitude conditions at 40,000 feet.

According to the present invention, it has been found that the life of a conventional metal-graphite sliding contacting element operating in atmospheres such as exist at sea level and at altitudes of at least 40,000 feet can be greatly lengthened and contact conditions materially improved if the brush composition is made from certain materials.

A brush embodying my invention is a metal-graphite 2 composition composed of 25 percent to percent copper, 10 percent to 60 percent graphite and 5 percent to 25 percent of at least one compound selected from the group consisting of barium fluoride, strontium carbonate and calcium carbonate, 0.1% to 5% boron nitride, and up to 10% in the aggregate of silver or lead or tin or rnix tures thereof. Coumarone indene resin may also be incorporated in the brush of the invention with or without the presence of the enumerated metals in a proportion of up to 5%. Generally, the sum of boron nitride, metal and resin used in the brush composition should be between 0.1 percent and 15.0 percent by weight of the brush. A preferred range for boron nitride is 0.5% to 1.5%. If the metals are present, a preferred range for the aggregate is 4% to 6%. Also, if the resin is present, the preferred range is 2% to 3%, all percentages being by weight of the brush.

The invention will be more fully understood from the following detailed description of typical examples of its use for prolonging brush life at sea level or high altitude conditions, it being understood that these examples are presented as illustrative only, and that they are not intended to limit the scope of the invention.

EXAMPLE I The composition of a copper-graphite mixture containing 75 parts copper, 15 parts graphite, 10 parts barium fluoride and a small amount of binder material was modified by adding to it 1 part boron nitride powder. The said ingredients were then well mixed and molded at a pressure of 15 tons per square inch to a block of suitable size for making a commutator brush. The block was then baked at 900 C. by suitable heating means for a period suflicient to impart known and inherent brush characteristics.

EXAMPLE II To a mixture having the composition of Example 1 containing 1 part boron nitride, was added 5 parts metallic silver powder. The mixture was formed into the shape of a commutator brush, and baked in the manner described in Example I to impart to it the requisite brush characteristics.

EXAMPLE 111 To a mixture having the composition of Example II containing 1 part boron nitride and 5 parts silver, there was added about 2.5 parts coumarone indene resin. The mixture was then formed and baked in the manner previously described.

The three additive compounds, whose performance it is sought to improve, are similar in a number of respects. Strontium carbonate, barium fluoride and calcium carbonate are all insoluble, non-deliquescent salts of alkaline earth metals. When added to a copper-graphite brush, the brush containing each salt has good friction properties and a minimum of sliding wear on the bearing surface.

Brushes embodying the invention have been made and tested at sea level and under condition-s simulating altitudes up to 60,000 feet above sea level. All tests were conducted by applying the brush to a machine having an operating speed of 6500 revolutions per minute and a rubbing speed of 5100 feet per minute. A brush spring pressure of 7.1 pounds per square inch was used. The current flow through the brush was adjusted to 20 or 40 amperes or a current density of about 60 or amperes per square inch depending upon the altitude. Tests were conducted in room air for a total of 20 hours or more. During that time readings were taken of contact voltage drop, brush temperature, and coefficient of friction. At the end of the tests brush length was measured and brush life in hours per inch of wear was calculated. All altitude tests were made on rotating copper rings.

'to current densities of 60 and 120 amperes per square inch *at sea level, and current densities of 60 and 120 amperes per square inch at 40,000 feet altitude.

Table l 1 Conventional brush composition.

The life measurement is an average obtained for altitudes from 20,000 feet to 60,000 feet. The time at 40,000 feet is predominating.

a N 01; tested.

From the data in Table I it will be seen that for a high altitude brush of the copper graphite type, herein disclosed, better performance can be obtained at sea level and under altitude conditions if the brush contains as additive material, predetermined quantities of either boron nitride alone or in combination with one or more members in the group consisting of silver, lead, tin, and conmarone indene resin. The improved performance manifests itself in relatively long brush life, small ring wear, generally lower coefiicient of friction, low operating tem- Composition by weight percent Brush Cu C BaF 51003 CaCO BN Ag Pb Sn Resin 15 75 15 10 0 0 0 0 0 0 74 15 O 0 1 0 0 0 0 69 10 0 0 1 6 0 0 0 68 14 9. 5 O 0 1 5 0 0 2. 5 45 45 10 0 0 0 0 0 0 0 45 45 9 0 0 1 0 0 0 0 42 42 10 0 0 1 5 O 0 0 42 42 10 0 0 l 0 5 0 0 42 42 10 0 0 1 0 0 5 0 47. 5 47. 5 0 5 0 0 0 0 0 0 47 47 0 5 0 1 0 0 0 0 44. 5 44. 5 0 5 0 1 5 0 0 0 44. 5 44. 5 0 5 0 1 o 5 0 0 44. 6 44. 5 0 5 0 1 0 0 5 0 47. 5 47. 6 0 0 5 O 0 0 0 0 47 47 0 0 5 1 0 0 0 0 44. 5 44. 5 O 0 5 1 5 0 0 0 X Conventional high altitude brush composition.

Operating Properties Brush Current Brush Cost. of

Density, Contact Brush Life, Friction Altitude Amps. Drop, Temp, Hrs. Against Per Volts 0. Per Copper Sq. Ft. Inch A 0 60 .14 95 895 3 NT 40,000 120 .24 70 425 .10 B 0 60 17 92 1, 455 NT 40, 000 120 32 72 745 10 C 0 60 13 98 1, 170 NT 40, 000 120 38 70 l, 000 103 D 0 60 23 88 2, 365 NT 40, 000 120 44 68 940 07 E 1 0 60 53 114 6, 800 NT 40, 000 60 .23 170 760 .35 F 0 60 1. 0 130 4, 300 N T 40, 000 60 55 146 4, 300 195 G 0 60 .45 126 6, 590 NT 40, 000 120 .88 120 3, 450 125 H 0 120 1. 29 138 5, 200 14 40, 000 120 l. 20 206 l, 900 16 I 0 60 56 121 9, 800 NT 40, 000 60 .65 166 880 19G J I 0 120 1.04 120 6, 300 18 40, 000 60 .25 87 858 19 K 0 120 94 103 8, 850 14 40, 000 60 39 108 1, 688 184 L 0 120 .92 88 11, 548 .09 40, 000 60 29 110 1, 070 178 M 0 120 1.07 131 11, 760 .16 40, 000 42 152 1, 000 161 N 0 120 .65 112 14,035 .10 40, 000 60 43 112 1, 565 170 O 1 0 120 .36 151 3, 050 .26 40, 000 60 48 140 1, 000 18 P 0 120 .73 120 5, 230 144 40, 000 60 60 05 1, 000 189 Q 0 120 1.00 114 5,100 133 60 4 peratures, high current load capacity and higher operating altitudes.

This application is a continuation-in-part of application Serial No. 493,070, filed March 8, 1955, now abandoned.

What is claimed is:

1. An' electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 0.1% to'5% boron nitride, 5% to 25% in the aggregate of at least one compound selected from the group consisting of barium fluoride, strontium carbonate and calcium carbonate, up to 5% coumarone indene resin and up to 10% in the aggregate of at least one metal selected from the group consisting of lead, silver and tin.

v2. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% of at least one compound selected from the group consisting of strontium carbonate, calcium carbonate and barium fluoride and 0.1% to 5% boron nitride.

3. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% of at least one compound selected from the group consisting of strontium carbonate, calcium carbonate and barium fluoride, 0.1% to 5% boron nitride and 1% to 10% in the aggregate of at least one metal selected from the group consisting of silver, lead and tin.

4. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% of at least one compound selected from the group consisting of strontium carbonate, calcium carbonate and barium fluoride, 0.1% to 5% boron nitride, 1% to 10% in the aggregate of at least one metal selected from the group consisting of silver, lead and tin, and 1% to 5% conmarone indene resin.

5. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% of at least one compound selected from the group consisting of strontium carbonate, calcium carbonate and barium fluoride, 0.1% to 5% boron nitride and 1% to 5% coumarone indene resin.

6. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% of a compound selected from the group consisting of strontium carbonate, calcium carbonate and barium fluoride, and additive material consisting of 0.1% to 5% boron nitride, up to 5% coumarone indene resin and up to 10% in the aggregate of at least one metal selected from the group consisting of lead, silver and tin, said additive material comprising 0.1% to 15% by weight of said brush.

7. An electrical contact brush adapted to operate efiiciently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% barium fluoride, 0.1% to 5% boron nitride, up to 5% coumarone indene resin and up to 10% of at least one metal selected from the group consisting of lead, tin, and silver.

8. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% barium fluoride and 0.1% to 5% boron nitride.

9. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% barium fluoride, 0.1% to 5% boron nitride and 1% to 10% silver.

10. An electrical contact brush adapted to operate efficiently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% barium fluoride, 0.1% to boron nitride and 1% to lead.

11. An electrical contact brush adapted to operate efliciently at altitudes of at least 40,000 feet consisting of to 75% copper, 10% to graphite, 5% to 25% barium fluoride, 0.1% to 5% boron nitride, 1% to 10% of at least one metal selected from the group consisting of tin, silver and lead and 1% to 5% coumarone indene resin.

12. An electrical contact brush adapted to operate efliciently at altitudes of at least 40,000 feet consisting of 25% to copper, 10% to 60% graphite, 5% to 25% barium fluoride, 0.1% to 5% boron nitride and 1% to 5% coumarone indene resin.

13. An electrical contact brush adapted to operate efliciently at altitudes of at least 40,000 feet consisting of 25% to 75% copper, 10% to 60% graphite, 5% to 25% barium fluoride, and additive material consisting of 0.1% to 5% boron nitride, up to 5% coumarone indene resin 6 and up to 10% of at least one metal selected from the group consisting of lead, tin, and silver, said additive material comprising 0.5% to 15% by weight of said brush.

References Cited in the file of this patent UNITED STATES PATENTS 1,121,960 Whitney Dec. 22, 1914 1,299,846 McCoy Apr. 8, 1919 2,156,803 Cooper et a1 May 2, 1939 2,445,003 Ramadanoff July 13, 1948 2,640,944 Ramadanofi June 2, 1953 2,731,371 Ramadanofi Jan. 17, 1956 2,739,254 Moberly Mar. 20, 1956 2,844,544 Ramadanoif July 22, 1958 FOREIGN PATENTS 712,188 Great Britain July 21, 1954 

1. AN ELECTRICAL CONTACT BRUSH ADAPTED TO OPERATE EFFICIENTLY AT ALTITUDES OF AT LEAST 40,000 FEET CONSISTING OF 25% TO 75% COPPER, 10% TO 60% GRAPHITE, 0.1% TO 5% BORON NITRIDE, 5% TO 25% IN THE AGGREGATE OF AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF BARIUM FLUORIDE, STRONTIUM CARBONATE AND CALCIUM CARBONATE, UP TO 5% COUMARONE INDENE RESIN AND UP TO 10% IN THE AGGREGATE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF LEAD, SILVER AND TIN. 